The current composition relates to hydrophobic vinylamine-containing polymers as paper softeners and dry strength aids and the processes for preparing them. In the current composition the primary amine groups of vinylamine-containing polymers are substituted with reactive hydrophobic functional groups and optionally with other reactive functional groups that impart physical characteristics of the polymers and provides applications properties to papermaking to soften paper products with no or minimal impact on paper dry strength properties.
Tissue and towel products are conventionally used as absorbent paper materials and softness of these products is an important physical property from customers' perspective. The softness sensation perceived by the consumer's hand (handfeel) comes from several paper properties including flexibility or stiffness of the paper sheet and the smoothness of the paper surface. Other major and critical physical properties of the paper products are the paper sheet tensile strength and water absorbency. The challenge in papermaking of the tissue and towel products is to balance these properties in order to produce a paper product with improved softness but not hurting the paper tensile strength and the water absorbance.
Traditional paper debonding agents including various imidazoline and ester quaternary derivatives can be applied as dispersions to papermaking fibers to disrupt cellulosic fiber-to-fiber binding, resulted in softer paper products. However, some of these low molecular weight (less than about 5,000 Daltons) hydrophobic cationic debonders such as quaternary imidazoline might cause irritation on human skin due to the exiting of residual toxic chemicals in the products that are highly controlled under governmental regulation. Furthermore, these types of debonding agents, when used as softeners, often cause significant decreases in paper tensile strength, and to such an extent in many cases that a dry strength resin needs to be used to compensate the strength loss in the paper sheet. In turn, using a dry strength resin could result in negatively affect paper softness. The dry strength resin not only complicates the papermaking process, but is also economically unfavorable. Although a significant amount of research and development efforts have been directed to the improvement of paper softness without affecting tensile strength, there is no single and good technical solution that can benefit both softness and tensile strength of the tissue or towel products.
A polymeric cationic softener is preferred in chemical design because it can be readily applied at the wet end in a papermaking process and still have good retention ability on the anionic cellulosic fiber. Structurally, the composition with high molecular weight softeners should possess the characteristics of the hydrophobic section as well as a hydrophilic section. One possible approach to constitute this type of structure is to modify a high molecular weight and hydrophilic water soluble cationic polymer using a reactive hydrophobic compound. The hydrophobic moiety can be appended to the polymer backbone in a random fashion or capped at both chain ends of the polymer.
U.S. Pat. No. 6,488,812 discloses new synthetic hydrophobic polymers having hydrogen bonding capability for reducing lint and slough in soft tissue products while maintaining softness and strength. US Patent Application No. 2003/0024669 discloses the use of hydrophobically modified polyaminoamides with polyethylene glycol esters in paper products to produce a softer and more absorbent paper material. U.S. Pat. No. 7,041,197 discloses a hydrophobically modified anionic polyelectrolyte and a method for making paper to enhance its wet strength without affecting paper softness.
Vinylamine-containing polymers are conventionally used in papermaking to improve dry strength of the paper products and to improve retention and drainage in papermaking processes. The primary amine groups of a vinylamine-containing polymer can be readily modified covalently as desired to introduce additional functionality to the polymer and alter its chemical and physical properties making it useful in other industrial applications as well as papermaking.
U.S. Pat. No. 5,292,441 discloses quaternized polyvinylamines obtained from the reaction with a quaternizing agent, such as methyl chloride, dimethyl sulfate, or benzyl chloride as flocculants and their use for wastewater clarification. U.S. Pat. No. 8,604,134 discloses modification of polyvinylamine with different functional groups and its application as a paper making additive. U.S. Pat. No. 7,902,312 discloses Michael adduct of polyvinyl amine with α, β-unsaturated alkyl carbonyl compounds and its subsequent use as an additive for paper making system. U.S. Pat. No. 5,994,449 discloses the use of vinylamine-vinyl alcohol copolymer functionalized with epichlorohydrin and its mixture with polyaminoamide as creping adhesive for paper application. U.S. Pat. No. 8,614,279 discloses a process for producing an acylated vinylamine-containing polymer.
Vinylamine-containing polymers are also used as base polymer for grafted polymerization of vinyl monomers. U.S. Pat. No. 6,864,330 discloses a PEG grafted polyvinylamine derivative. U.S. Pat. No. 5,753,759 discloses graft copolymers of vinylamine based polymers. US Patent Application No. 2015/0299961 discloses a graft copolymer composition of a vinyl monomer and a functionalized vinylamine-containing base polymer and a method of preparing the graft copolymer.
Although some of the above references disclose modified vinylamine-containing polymers, they do not disclose the current hydrophobically modified polyvinylamines, which can be used as papermaking dry strength additives, retention aids, drainage aids or pitch and stickies control agents. Nor, do any of the references disclose hydrophobic polyvinylamine derivatives in papermaking. Through extensive research it was found that hydrophobically modified vinylamine-containing polymers can enhance paper softness without negatively impacting paper dry strength properties.